In recent years, there have been increasing demands on mobile wireless or radio devices such as portable telephone sets. As a conventional type antenna for portable telephone, a whip antenna is often used, which can be located in a portable telephone main unit.
As an example, FIG. 33 and FIG. 34 each represents an arrangement of a conventional type antenna system as disclosed, for example, in JP-A-1-204504. In the figures, symbols and component names described in JP-A-1-204504 are used. As shown in FIG. 33, when an antenna element 14 is withdrawn from a portable telephone main unit 10, a contact member 15 comes into contact with an upper contact piece 21a. As a result, the antenna element 14 is connected to a matching circuit assembly 12.
As shown in FIG. 34, when the antenna element 14 is located in the portable telephone main unit 10, a contact member 16 is brought into contact with a lower contact piece 21b. As a result, the antenna element 14 is connected to the matching circuit assembly 12. Thus, the antenna element 14 is connected to the matching circuit assembly 12, not only when it is withdrawn from the portable telephone main unit 10 but also when it is located in it.
In the above arrangement, it is supposed that, when the antenna element 14 is withdrawn from the portable telephone main unit 10, impedance is Z1 when the antenna element 14 is seen from the matching circuit assembly 12 and impedance is Z2 when the antenna element 14 is seen from the matching circuit assembly 12 with the antenna element 14 located in the portable telephone main unit 10. If element length of the antenna element 14, position of feeding point, and dimensions of wireless device housing are adjusted in such a manner that Z1 and Z2 become equal to each other, satisfactory matching condition can be attained by the matching circuit assembly 12 in both cases, i.e. in case the antenna element 14 is withdrawn from the portable telephone main unit 10 or in case it is located in the portable telephone main unit 10. As a result, mobile communication with high quality and stability can be achieved.
The conventional system is disadvantageous in that, when the antenna element 14 is located in the portable telephone main unit 10, a part of radiation energy is absorbed by the telephone main unit or to the body of a person who carries the telephone, and the characteristics of the antenna are deteriorated.
As one of the measures to solve this problem, a separate type helical-whip antenna is often used, in which the antenna is separated to two types of antenna, i.e. to a helical antenna operated when the antenna is located in the portable telephone main unit and a whip antenna operated when the antenna is withdrawn from the portable telephone main unit. FIG. 35A to FIG. 35C each represents an arrangement example of such an antenna system. FIG. 35A shows an entire arrangement of a separate type helical-whip antenna, and FIG. 35B and FIG. 35C show respectively the condition when the antenna 30 is located in the telephone main unit 38 and the condition when the antenna 30 is withdrawn from the telephone main unit 38.
As shown in FIG. 35B, when the antenna 30 is located in the telephone main unit 38, a helical antenna 31 is connected to a connection terminal 37 leading to a radio circuit via a feeding unit 32, a connection member 35, and a matching circuit 36. In this case, a whip antenna 33 located in the telephone main unit is separated from the radio circuit, and no influence is exerted on the radio circuit from the telephone set around the whip antenna the body of a person who carries the telephone.
As shown in FIG. 35C, when the antenna 30 is withdrawn from the telephone main unit 38, the whip antenna 33 is connected to the connection terminal 37 leading to the radio circuit via a feeding unit 34, the connection member 35, and the matching circuit 36. By adopting such an arrangement, it is possible to separate the antenna to two types, i.e. to an antenna operated when it is located in the telephone main unit and to an antenna to be operated when it is withdrawn from the telephone main unit, and deterioration of the characteristics of the antenna when the antenna is located in the telephone main unit can be avoided.
However, there are problems in that element length of the antenna 30 is increased by the helical antenna 31 and that strength of the connecting point of the helical antenna 31 and the whip antenna 33 is weakened. In the conventional type antenna, impedance is determined by equivalent electrical length such as element length of the antenna element or dimensions of the radio circuit housing. Accordingly, it is disadvantageous in that the desired impedance and external design of the radio circuit are not necessarily compatible with each other.
Further, with the diversification of the mobile communication system, frequency band used is also diversified, e.g. 800 MHz band, 1.5 GHz band, and 1.9 GHz band, and there are strong demands on the development of a radio circuit, which can be used for different frequency bands. The conventional type antenna system can cope with only one frequency band, and if it is used for a wireless device for two or more different systems, characteristics are extremely deteriorated.